High energy fuel



United Sttes HIGH, ENERGY FUEL Robert L. McLaughlin, Woodbury, Lawrence 0. Miller, Glassboro, and John W. Schick, Merchantville, N.J., assrgnors toSocony Mobil. Oil Company, Inc., a corporation of New York No Drawing. Filed May 19, 1959, Ser. No. 814,145

3 Claims. (c1. 60--35.4)

This invention relates to high energy jet combustion fuel. It is more particularly concerned with agents for increasing the energy content of jet combustion fuels.

As is well knownto those familiar with the art, the range or payload of supersonic aircraft powered by jet engines or turboprop engines is limited by the energy content of the fuel used. The conventional hydrocarbon jet fuels, meeting the specifications set forth in military specifications as defined hereinafter, usually have a relatively low volumetric net heat of combustion in the order of 115,000 to 126,000 B.t.u./gal. and a weight energy content not much over the minimum of about 18,400 B.t.u./lb. Efforts to increase the B.t.u./ gal. have been accompanied by unfavorable decreases in B.t.u./lb.

Many supersonic aircraft are limited by the volume of fuel that can be carried in the tanks. Thus, increased energy content per gallon will result in increased operational range or payload. It is highly desirable, therefore, to have jet fuels that have increased volumetric energy content without sacrifice of other conventional characteristics of the jet fuel. Another advantage of fuels of this type is their excellent thermal stability. Any gain in the thermal stability of the fuel allows less weight for insulating or for refrigerating equipment and, therefore, more range or payload.

It has now been discovered that volumetric energy can be added to jet fuels without detracting from the other conventional characteristics. It has been discovered that the addition of a certain hydrocarbon compound to conventional hydrocarbon jet fuels will increase the number of B.t.u. per gallon without substantial effect on the number of B.t.u. per pound. It has also been discovered that this hydrocarbon can be used as the sole fuel in certain cases.

Accordingly, it is a broad object of this. invention to provide a high energy fuel. Another object is to provide a jet fuel of increased number of B.t.u. per gallon. A specific object is to provide a jet fuel containing a specific hydrocarbon compound to increase the volumetric energy content thereof. Another specific object is to provide a means to use the specific hydrocarbon compound as the sole fuel in certain cases. Other objects and advantages of this invention will become apparent to those skilled in the art, from the following detailed description.

In general, this invention provides a high energy jet combustion fuel that comprises a hydrocarbon jet fuel containing an amount, suflicient to increase the volumetric energy content thereof, of 1,1,3-trimethyl-3-cyclohexylhydrindane. Another embodiment of this invention provides, in the operation of jet propelled aircraft that attain supersonic speeds with subsequent high aerodynamic heating, that l,1,3-trimethyl-3-cyclohexylhydrindane be stored Patented Dec. 13, 19 60 ice in the wings of the aircraft to absorb aerodynamic heat from the wings and to be used as a high energy fuel in flight.

The addition agent utilizable in this invention is 1,1,3- trimethyl-3-cyclohexylhydrindane. This material is readily prepared by hydrogenating, by usual hydrogenation methods, 1,1,3-trimethyl-3-phenylindane. The latter can be prepared most feasibly" by dimerizing alpha-methylstyrene to the cyclic dimer. Several methods of making the cyclic dimer are known, but a very efficient method is described in copending application Serial No. 803,080, filed March 31, 1959. It will be recognized, however, that the manner of preparing the addition agent contemplated herein is not a limiting factor of this invention, as any method of preparation or any source of the material can be used.

The conventional hydrocarbon fuels that are improved in accordance with this invention are hydrocarbon fractions' having an initial boiling point of at least about F. and an end boiling point as high as about 750 F. T-hese fuels can be made up of straight-run distillate fractions, catalytically or thermally cracked (including hydrocracked) distillate fractions, or mixtures of straightrun fuel oil, naphtha, etc. with cracked distillate stocks, alkylate, and the like. The principal properties that characterize the jet fuels is their boiling range. Each fuel will have a boiling range which falls within the aforespecified range. Specifications that define typical specific fuels are MIL-F-56l6, MIL-J-5624D, MIL-F-25656, MIL-F-2524A, MIL-F-2557 6A, MIL-1 2555 8B, and MIL-J-S 161E.

The amount of 1,l,3-trimethyl-3-cyclohexylhydrindane that is added to the jet fuels will depend upon the amount of added energy desired and required. In general, an amount as small as about 13 percent, by weight of the fuel, and as much as about 59 percent, by weight, can be added. Larger amounts will be effective from the standpoint of adding energy, but will tend to increase the viscosity of the fuel beyond desirable limits. In practice, between about 13 percent and about 30 percent, by weight of the finished fuel can be used.

In most cases, the 1,1,3-trimethyl-3-cyclohexylhydrindane will be blended with the conventional jet fuel before it is loaded into the tanks ready for use, i.e., at the refinery, storage depot, or even at the airstrip just prior to loading the jet vehicle. As was mentioned hereinbefore, however, it is also contemplated to use 1,1,3-trimethyl-3- cyclohexylhydrindane alone. The 1,1,3-trimethyl-3-cyclohexylhydrindane has a pour point of about 10 F. Accordingly, it is not utilizable alone as a fuel in many jet aircraft, because it would not how at temperatures encountered at high altitudes. In supersonic aircraft, however, the high speeds cause aerodynamic heating of the wings. In such aircraft, the l,1,3-trirnethyl-3-cyclohexylhydrindane can be stored in the wings. A conventional fuel, such as JP-S or JP-6 would be used for low speed flight during takeoff and landing. Then, as the wings are heated by aerodynamic heating and the 1,1,3-trirnethyl-3- cyclohexylhydrindane becomes more fluid, it is used as the sole fuel. The aircraft, in this case, is equipped with two fuel systems and means to switch from one fuel to another.

EXAMPLES 1 AND 2 Two blends of 1,1,3-trimethyl-3-cyclohexylhydrindane in a typical conventional JP-S jet fuel were prepared. The base jet fuel had the properties set forth in the table.

Blend proportions and properties of theblends are also set forth in the table.

Table Base Exailmple Exagiple Composition, Vol. percent: A 1,li3-trimethyl-3-cyclohexylhydrin- Gravity, API ASIM Distillation,

I.B.P

.E.P Aniline Point, F Freeze Point, F Viscosity, 0%.

Net Heat of Combustion;

B.t.u./lb B.t.uJgal. 60 F Smoke Poiut,,mm

Luminosity Number (CRO Lulu i nometer); 43 t 44 In order to obtain the values in the table, standard test methods were used, as defined in military specifications. It Will be noted that the addition of 1,1,3-trimethyl-3- cyclohexylhydrindane has greatly increased the B.t.u./ gal.

without greatly decreasing the B.t.u./lb. This gives the fuel blend added energy which results in increased range or payload when the fuel is used in jet space-limited aircraft. I

Although the present invention has been described with preferred embodiments, it isto be. understood that modia fications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

What is claimed is:

1. An improved method of operating supersonic jet aircraft that comprises placing 1,1,3-trimethyl-3-cyclohexylhydrindane in the wings of said aircraft, and operating on conventional hydrocarbon jet fuel during takeoff and until supersonic speeds are attained, and as supersonic speeds effect aerodynamic heating of the wings, discontinuing the use of conventional fuel and operating said aircraft onsaid 1,1,3-trimethyl-3-cyclohexylhydrindane as the sole fuel. v

2.. A high energy jet combustion fuel that consists essentially of a hydrocarbon fraction having an initial boiling point of at least about 100, F. and an end boiling point as high as about 750 F. containing between about 13 volume percent and about 59 volume percent of 1,1,3-

7 I trimethyl-3 -cyclohexylhydrindane. I

.3. A high energy jet combustion fuel that consists essentially of a hydrocarbon fraction having an initial boiling point of at least about 100 F. and an end boiling point as high as about 750 F. containing between about 13 volume percent and about 30 volume percent of 1,1,3- trimethyl-3-cyclohexylhydrindane.

No references cited. 

1. AN IMPROVED METHOD OF OPERATING SUPERSONIC JET AIRCRAFT THAT COMPRISES PLACING 1,1,3-TRIMETHYL-3-CYCLOHEXYLHYDRINDANE IN THE WINGS OF SAID AIRCRAFT, AND OPERATING ON CONVENTIONAL HYDROCARBON JET FUEL DURING TAKEOFF AND UNTIL SUPERSONIC SPEEDS, ARE ATTAINED, AND AS SUPERSONIC SPEEDS EFFECT AERODYNAMIC HEATING OF THE WINGS, DISCONTINUING THE USE OF CONVENTIONAL FUEL AND OPERATING SAID AIRCRAFT ON SAID 1,1,3-TRIMETHYL-3-CYCLOHEXYLHYDRINDANE AS THE SOLE FUEL. 